Street and area lights are installed to provide illumination for safety, recreation, and other purposes. The lights are typically controlled for dusk-to-dawn operation by individual photoelectric controls, timers/contactors (controlling strings of lights), or a power line carrier. The installed base of street lights mostly use gas lighting elements such as mercury vapor lamps, high-pressure sodium vapor lamps, and metal halide lamps. These lamps can only accommodate minimal dimming, with only minimal corresponding savings in energy/cost. As such, the housings, wiring, and other electronics of this installed based typically provides only for on and off operation. More specifically, the present photoelectric controls for street lights typically provide on and off operation through two-wire or three-wire connections, which may be coupled to the light through a NEMA locking three prong receptacle and twist lock or the like. Direct wired photoelectric devices are also sometimes used, as are built-in or attached timers. However, these existing devices uniformly provide simple on/off control to the street light.
By contrast, the intensity of arrays of high-powered LEDs can be easily controlled simply by varying DC current or voltage, or using pulse width modulation (PWM) or other techniques. As the brightness and efficiency of LEDs has improved, LED technology is becoming a suitable candidate for street and area lighting. In this context, full light is not required at all times and dimming the lights could save considerable electricity, even though existing light fixtures do not accommodate this type of variable control.
There remains a need for variable control of LED lights adapted to existing street light infrastructure.